More than even before, consumers are enjoying the convenience of listening to music, watching a video, or simply carrying on a telephone conversation using portable digital media devices. Devices such as consumer grade cellular telephone handsets, palm-sized or laptop computers with wireless data networking capability, and handheld digital media players such as MP3 and DVD players, are delivering ever improving sound quality to their users.
To verify the performance of a cellular telephone handset, including the acoustic capabilities of its built-in receiver (also referred to here as earpiece), a manufacturer typically builds or purchases a test fixture for testing the audio and radio frequency (RF) functionalities of the handset. Reliable test results can be ensured by first calibrating the test fixture prior to using it for testing a device.
An acoustic measurement system or test fixture has a microphone that needs to be calibrated prior to use. Typically, the microphone is first removed from the system, and then calibrated outside the system. A reference acoustic pressure source is attached to the microphone, and then the signal produced by the microphone is measured. The measurement is stored as a reference value associated with the particular microphone, and a related electronic circuit (or microphone reading) may then be adjusted accordingly for future readings, to obtain the calibrated response from the microphone. The microphone is then installed back into the measurement system with the expectation that the system is now ready to reliably test the media devices.